In most underground mines, ground anchors form the basis of the primary roof and/or wall support systems within tunnels. To enforce a roof or wall, ground anchors can be installed mechanically or manually using resin, cement grout, friction anchors or point anchors or a combination of such. It has been estimated that 30%-35% of the rock anchors do not perform to specification and may represent some risk to the maintenance of a safe workplace environment (Galvin et al 2001).
Typically the method for installing chemical anchors, otherwise known as resin anchors, first requires for a hole to be drilled into the roof or wall. Resin anchors comprise steel bolts/cables which when in position are encased in a resin within the drill hole. The resin protects the bolt from the corrosive influences within the drill hole and penetrates the surrounding rock formation to adhesively unite the strata and hold the steel bolt in position.
The resin is typically supplied in a cylindrical two component cartridge which comprises a resin component and a resin catalyst component. In use the cartridge is manually inserted into a drilled hole and the steel bolt/cable is then inserted into the hole. The insertion of the bolt causes the plastic sheath of the cartridge to break. The steel bolt is then rotated to shred the cartridge, mix the resin components and disperse the resin. The resin mixture fills the annular area between the drill hole wall and the shaft of the steel bolt. The mixed resin cures and binds the steel bolt to the surrounding rock strata.
Breaking the plastic sheath of the cartridge and mixing the resin components effectively can be problematic. Many resin anchors are ineffective because the resin components are not mixed completely. The shredded cartridge can interfere with the resin and catalyst mixing. Poor mixing results in an inferior cured resin and results in poor bond strength between the bolt and drill hole wall. Furthermore this method of installing resin anchors is complicated and time-consuming. The method requires a mineworker to be positioned in the non-supported portion of tunnel for the manual insertion of the resin cartridge. The method results in slow resin anchor installation and provides for workplace safety issues.
A single-stage self-drilling resin anchor system has been proposed as a solution to overcome the aforementioned limitations. This system utilises a hollow bar with a passage through the centre of the bar serving as a flowpath for water. A cavity is provided at the centre of the bar for housing the resin cartridge. In this system, after the drill hole has been completed, water is injected into the cavity containing the resin cartridge. The water ruptures the resin cartridge, forcing resin through a hole in the tip of the bar into the drill hole with the steel bolt. The resin then sets, bonding the bolt to the rock strata.
A disadvantage with this system is that the resin cartridge may prematurely rupture during transportation, or during the boring process, prior to completion of the boring process. A further problem is that there may not be sufficient resin forced into the hole for securing the steel bolt.
A dedicated drill rig has also been proposed. This system has a dedicated drill and installation platform where the hole is drilled, a resin injector guide tube is indexed over to the drilled hole and the resin is fired into the drilled hole. Once the resin is fired into the hole then the ground anchor is indexed across and installed into the drilled hole. Throughout this process, the drill component is stationary. This rig provides a very good process for ground support installation. However, because it is a dedicated machine it is very expensive for a mining business to incorporate into their fleet as it cannot perform any other function apart from ground support installation. Further, the resin cartridge can break open causing the two chemicals to mix and form into a solid mass, and thereby blocking off the hole and stopping the ground anchor from entering the drilled hole.
From the above description of several prior art methods of installing ground anchors it can be seen that the prior art systems utilised suffer from issues associated with at least resin stability and effective mixing of resin components once in use. Various safety issues also arise. Therefore, the present invention was developed with a view to providing a simple and effective method and apparatus for injecting resin for use during the installation of resin anchors.
References to prior art in this specification are provided for illustrative purposes only and are not to be taken as an admission that such prior art is part of the common general knowledge in Australia or elsewhere.